alt Hacker Newsimho the vaunted readability of custom elements has long been available with haml, with added readability by virtue of the indentation rules replacing closing tags. Not sure why it didn't really gain much traction, maybe the pre-processing is problematic when there's no server-side framework like Rails?
Either everyone uses HAML or no one does IMO.
Developers like to copy/paste UI component example HTML from Tailwind/Bootstrap documentation, they like predictability/portability. They don't want a project that's half HTML and half HAML...ie, Vue/React using HTML/JSX vs 50% of Rails views in HAML, 50% old ones in HTML.
Just like how using Vanilla JS is much smoother and reliable than using the latest wrapper framework.